1. Field of the Invention
The present invention relates to a bonding device and a bonding tool for electronic parts for bonding an object to be bonded such as the electronic parts to a surface to be bonded such as an electrode of a board.
2. Description of the Related Art
As a method for bonding an object to be bonded such as electronic parts to a surface to be bonded such as an electrode of a board, a method using an ultrasonic pressure welding is known. According to this method, while the electronic parts are pressed to the surface to be bonded, an ultrasonic vibration is applied to the electronic parts to fractionally vibrate the surface to be bonded and to allow the surface to be bonded to come in to close contact with the electronic parts. The bonding tool used in this method has an elongated horn for transmitting the vibration of a vibration generation source to the electronic parts. While a load and a vibration are allowed to act on the electronic parts by a bonding operation part provided in this horn, the electronic parts are allowed to come into contact under pressure with the surface to be bonded. Thus, the electronic parts are bonded to the surface to be bonded.
As such a bonding tool, a bonding tool having a heater incorporated in a horn has been known. Thus, electronic parts can be advantageously heated through a bonding operation part upon boding so that a bonding efficiency can be improved. As a method for mounting such a heater on the horn, a method has been hitherto employed that a rod shaped heater is inserted and fixed to a mounting hole provided in the direction perpendicular to the longitudinal direction of the horn (for instance, see JP-A-2000-200961 (FIG. 3)).
In bonding the electronic parts, to assure a stable bonding quality, the propagation characteristics of the ultrasonic vibration transmitted to the horn from the vibration generation source need to be stabilized to constantly apply a stable vibration to the electronic parts. However, when the above-described usual method for mounting the heater is directly applied to the bonding tool for which the stable vibration characteristics are requested, such problems as described below arise.
Firstly, in the usual structure, since the rod shaped heater is inserted transversely in a vibration propagating direction, the propagation of vibration is apt to be interrupted by the heater. Especially, when a large heater is combined with a horn of a small size employed for compact electronic parts, the above-described influence obviously occurs. Accordingly, in the usual bonding tool, a heating operation with high efficiency has been hardly compatible with the realization of stable vibration characteristics.
Further, in the usual structure, while the rod shaped heater is inserted into the mounting hole, the heater is fixed to the horn. Thus, the heater is always pressed to the inner surface of the mounting hole. However, contact pressure under which the heater is pressed to the inner surface of the mounting hole is not always constant and frequently changes due to a temperature change or the unfastened state of fastening means. Accordingly, the rigidity distribution of the whole of the horn is sometimes varied so that stable vibration characteristics may not be undesirably held.